1. Technical Field
The present invention relates to a polyethylene composition for use in insulations and joints of extra-high voltage power cables, and to an extra-high voltage power cable and a joint using this polyethylene composition. In particular, the present invention relates to a cross-linking polyethylene composition having an extremely small amount of dielectric loss which is highly suitable for use in insulations and the like of extra-high voltage power cables of 275 kV or more.
2. Background Art
Conventionally, cross-linking polyethylene compositions were known in which an organic peroxide such as dicumyl peroxide or the like was added to low density polyethylene as a cross-linking agent, this was mixed and heated, and thus caused to cross-link; as a result of the superior characteristics thereof, such as the resistance to heat, and the electrically insulating properties, and the like, such compositions were widely employed as insulationss for electric power cables.
However, in cases in which power cables employing conventional cross-linked polyethylene compositions as insulations were used in the power transmission of extra-high voltage alternating current of 275 kV or more, the highest temperature during normal service reached 90.degree. C. and the electric field stress exceeded 20 kV/mm, so that there was a problem in that dielectric loss was large, and it was thus difficult to use such power cables.